PERMANENT MAGNETIC Fe-Mn-Cr ALLOY CONTAINING NITROGEN

ABSTRACT

A permanent magnetic alloy consists essentially of 0.05 - 0.5 wt. percent N, 5- 15 wt. percent Mn, 2- 12 wt. percent Cr, and remainder iron, produced by solution treatment at a temperature not lower than 900*C, cold rolling to a thickness reduction of 10- 98 percent and if desired, aging at 100* - 800*C. The alloy may additionally contain Mo, Co, A1, C, Nb, Ti, Zr and V.

ilrnted States Patent 11 1 1111 3,836,406

Yoda Sept. 17, 1974 [54] PERMANENT MAGNETIC Fe-Mn-Cr ALLOY [56]References Cited CONTAINING NITROGEN UNITED STATES PATENTS [75]Inventor: Renpei Yoda, Kawasaki, Japan 2,382,651 8/1945 Nesbitt 148/3157958 [73] Asslgnee: The 91mm of Natlmal Research 5,232,336 ii959 75/126Institute for Metals, Tokyo, Japan 2,948,604 8/1960 MacFarlane et a175/126 [22] Filed: Dec. 211, 1973 Primary Examiner-Walter R. Satterfield[21] Appl. No.: 427,361

Related US. Application Data [57] ABSTRACT [63] Continuation of Ser. No.325,305, Jan. 22, 1973, A permanent magnetic alloy consists essentiallyof abandoned, which is a continuation of Ser. No. 0.05 0.5 wt. percentN, Wt. percent Mn, 2- 12 g- 1970, abandofledwt. percent Cr, andremainder iron, produced by solution treatment at a temperature notlower than 900C, 1 [LS 126 126 cold rolling to a thickness reduction of10- 98 percent [51] '1 Cl 75/126 i{ /f and if desired, aging at 100800C.

nt. 01 58 Field of Search 75/126 B, 126 J, 126 N, The alloy may addmnauyComm Nb, Ti, Zr and V.

1 Claim, 2 Drawing Figures PATENIED 3.836.406

FIG. 2

TORC L (ERG/Cm FLUX DENSITY (G) 1 1 l 1 I 1 I20 I00 8O 60 4C) 20 OMAGNETIZING FORCE(O) E 1 PERMANENT MAGNETIC Fe-Mn-Cr ALLOY CONTAININGNITROGEN This application is a continuation of application Ser. No.325,305, filed Jan. 22, 1973, which is a continuation of applicationSer. No. 60,858, filed'Aug. 7, 1970, both now abandoned.

This invention relates to a permanent magnetic alloy, and moreparticularly, to a permanent magnetic alloy mainly composed of Fe-Mn-Cr,containing nitrogen, and if desired, at least one of Mo, Co, Al, Nb, Ti,Zr, V and C being added thereto, produced by solution treatment over900C, cold rolling, and if desired aging.

The permanent magnetic alloy has excellent permanent magneticcharacteristics, high cold rolling property and does not containexpensive elements, and even if they are contained, the amount of themis so small that the cost is very low.

In general, magnetic characteristics of permanent magnet is shown byresidual flux density. Br, coercive force He, maximum energy product andthe like. The

\ higher these values, the stronger the magnet. Representative exampleis Alnico magnet mainly composed of Fe-Ni-Co-Al-Cu. However, Alnicomagnet contains expensive and not easily available elements such asnickel, cobalt and the like. In addition, alnico magnet isdisadvantageously so rigid and brittle that neither forging, rolling,lathing nor punching is possible. Only grinding working can be employed.However, it is often requested to use a permanent magnet in a form ofthin plate and fine wire and it is desired that a permanent magnet hasplastic workability such as bending and press punching.

Sometimes a permanent magnet having relatively low coercive force suchas so-called semi-hard magnet is required. The permanent magnetaccording to this in vention is very useful for such request.

Heretofore, there have been known Vicalloy and Cunife" which can becold-rolled to produce wire and thin plate.

Further it is also known that an extensive cold rolling of 18-8stainless steel containing 18 percent Cr and 8 percent Ni results inrevealing of permanent magnet property, and the permanent magnet thusproduced has been used as a recording wire material for a wire recorder.However, these alloys also need expensive and not easily availablenickel and cobalt in an large amount. Therefore, they are used only inspecial fields such as special motors, miniature motors and magneticmemory elements.

It is clearly desirable to produce the abovementioned permanent magnetsin a large amount at low cost in view of the recent development ofelectronic device and automation devices.

Heretofore, an iron alloy containing about 12 percent Mn and 1 to 1.3percent C (not containing Ni and Co) and having workability, so-calledHadfield steel, has been known. This steel is not magnetic at a stage ofsolution treatment, but becomes ferromagnetic by cold rolling to showpermanent magnet property. The magnetic behavior in the cold rollingstep is explained as follows. The steel becomes non-magnetic y-phase bysolution treatment from metallographical point of view and the coldrolling converts the phase to a-phase resulting in ferromagneticproperty.

Furthermore, such steel containing manganese causes a-transformation ata relatively low degree of working to be hardened so that this steel hasbeen widely used as a material of antiabrasion tool, but hardly used asa magnetic material.

According to this invention, the cold rolling causes 'ya transformationof the Fe-Mn system alloy and further Cr (accelerating(it-transformation) and nitrogen (stabilizing 'y-phase) are incorporatedto the alloy at an appropriate ratio so as to control amount of a-phaseproduced by cold rolling. Therefore, Br and I-Ic contributing topermanent magnetic characteristic can be optionally controlled.

An important feature of the alloy of this invention is that nitrogen isused as a component of the alloy though nitrogen has never been used asa component of magnetic material andno advantage of incorporation ofnitrogen has never been found. In general, when a metal is molten inair, nitrogen in air is dissolved in the metal, but the amount ofnitrogen thus incorporated is only less than 0.1 percent.

Nitrogen is a most important element affecting the characteristics ofalloy of this invention. When the nitrogen content is less than 0.05percent, a-phase amounts to a large content and the cold rollingproperty is not improved while at a nitrogen content exceeding 0.5percent the magnetic property is deteriorated. Therefore, nitrogencontent ranging from 0.05 to 0.5 percent is selected according to thisinvention.

When the manganese content is less than 5 percent, a large amount ofa-phase is already present after the solution treatment so that the coldrolling property is hardly present while at a manganese contentexceeding 15 percent the magnetic property is lowered. Thus, the presentinvention defines the manganese content as from 5 to 15 percent.

When the chromium content is less than 2 percent, the magnetic propertyis not remarkably improved by the cold rolling while at a chromiumcontent exceeding 12 percent the cold rolling property is lowered.Therefore, chromium content ranging from 2 to 12 percent is employed inthis invention.

The cold rolling is not markedly deteriorated by not more .than 4 weightpercent molybdenum, not more than 12 weight percent cobalt, not morethan 2 weight percent aluminum, not more than 3 weight percent niobium,titanium, zirconium, and vanadium, and these elements added singly or incombination, improve magnetic property. With respect to amounts of theseelements and the carbon below, a part of the iron weight percent isreplaced by the total weight percent of these elements and carbon added.

With respect to carbon, a carbon content up to 0.4 percent canremarkably improve the cold rolling without deterioration of magneticproperty.

.According to this invention, magnetic property of the alloy can becontrolled by selecting the chemical components and further the a-phaseformed by the cold rolling is inversely transformed to y-phase by theaging treatment so that the amount ratio of a-phase and 'y-phase can beoptionally controlled by selecting the aging conditions, and the Br canbe markedly increased by recrystallization.

According to another aspect of this invention, there is provided apermanent magnetic alloy consisting essentially of from 0.05 to 0.5weight percent nitrogen, from 5 to 15 weight percent manganese, from 2to 12 weight percent chromium, and remainder iron, pro duced by hotworking at a temperature not lower than 900C accompanied with solutiontreatment, cold rolling resulting in a thickness reduction of to 98percent, and if desired, aging. Further, this alloy may con tain Mo, Co,Al, Nb, Ti, Zr, V and C as previously mentioned.

The hot working is effected at a temperature not lower than 900C andthen quenched to cause a solution treatment effect.

The present invention will be further described referring to the drawingin which:

FlG. 1 shows a demagnetizing curve of permanent magnetic alloy accordingto this invention; and

FIG. 2 shows a magnetic torc curve of permanent magnetic alloy accordingto this invention.

Referring to FIG. 1 the demagnetizing curves are those for permanentmagnetic alloys composed of 0.227 weight percent nitrogen, 11.11 weightpercent Mn, 9.17 weight percent Cr, 2.16 weight percent Mo, 1.18 weightpercent Al and remainder iron produced by solution treatment, coldrolling to a thickness reduction of 50 percent and aging treatment atvarious temperatures. The temperature shown in the graph is atemperature at which the aging treatment is effected. The AS ROLLEDmeans the alloy shown by the curve is subjected to solution treatmentand cold rolling, but not aging.

The phase formed by cold rolling is reversely transformed to y-phase byaging. Therefore, the amount ratio of a-phase to y-phase can beoptionally controlled and the Br can be remarkably increased byrecrystallization as shown in FIG. 1.

Referring to FIG. 2, the magnetic torc is that of permanent magneticalloy composed of 0.169 weight percent nitrogen, 9.20 weight percent Mn,8.62 weight percent Cr, 1.62 weight percent Mo, 5.21 weight percent Coand remainder iron, produced by solution treatment, cold rolling to athickness reduction of 55 percent, and aging at 500C.

The abscissa of FIG. 2 represents an angle between a cold rollingdirection and a magnetizing direction.

As is clear from FIG. 2, the permanent magnetic alloy has a rollingeffect having the magnet easy axis to the direction of rolling.

The following Example is given for illustrating the present invention,but, by no means, should be construed as restricting the presentinvention.

EXAMPLE As the starting metal, an electrolytic iron was used, and anitrided manganese containing 6 percent nitrogen and a nitrogencontaining ferrochrome containing 40 percent Cr and 6.5 percent N wereemployed for adding Mn, Cr as well as N to the electrolytic iron. Carbonwas added by using ferro-carbon containing 4 percent C, and as Mo, Co,and Al, each commercially available pure metal is used.

Allous containing various ratio of components were prepared by using ahigh frequency electric furnace, and an ingot obtained by molding wasforged at 1,150C and then made into a thin plate of 5mm. thick at 1,000Cby hotrolling to prepare samples.

The samples were subjected to a solution treatment by heating at 1,050Cfor 30 minutes and cooling with water. And then cold rolling at variousworking ratio was effected. The samples thus treated were compared withsamples which were subjected to aging at C to 900C for one hour inaddition to the above mentioned treatments with respect to Br and Ho byusing a automatic recording flux meter.

Representative results are shown below.

1. An alloy composed of 0.222 weight percent nitrogen, 11.03 weightpercent Mn, 9.72 weight percent Cr, 2.04 weight percent Mo, andremainder iron was subjected to solution treatment at 1,030C and then tocold rolling resulting in a thickness reduction of 50 percent. The alloythus treated has a residual flux density, Br, of 6,700 gauss (G) and acoercive force, HC, of 44 oersteds (0e).

2. When the above-mentioned alloy was cold rolled to a thicknessreduction of 75 percent in place of 50 percent, the alloy thus coldrolled had a residual flux density, Br, of 8,900 G and a coercive force,Hc, of 56 0e.

3. The alloy obtained in (2) above was subjected to aging at 500C for 1hour. The resulting alloy had a residual flux density, Br, of. 10,700 Gand a coercive force, He, of 56 0e.

4. The alloy obtained in (2) above was subjected to aging at 600C for 1hour. The alloy thus aged had a residual flux density, Br, of 2,400 Gand a coercive force, Hc, of 0e.

5. An alloy composed of 0.301 weight percent nitro gen, 10.12 weightpercent Mn, 9.63 weight percent Cr, 2.10 weight percent Mo and remainderiron was subjected to solution treatment at 1,050C and then cold rolledto a thickness reduction of 75 percent. The resulting alloy had aresidual flux density, Br, of 8,200 G and a coercive force, He, of 490e.

6. The alloy obtained in (5) above was subjected to aging at 500C for 1hour. The alloy thus aged had a residual flux density, Br, of 12,300 Gand a coercive force, He, of 60 0e.

7. An alloy composed of 0.227 weight percent nitrogen, 1 1.1 1 weightpercent Mn, 9.17 weight percent Cr, 2.10 weight percent Mo, 1.18 weightpercent Al and remainder iron was subjected to a solution treatment at1,050C, cold rolled to a thickness reduction of 75 percent, and aged at500C for 1 hour. The resulting alloy had a residual flux density, Br, of12,300 G and a coercive force, lie, of 50 0e.

8. The starting alloy as used in (7) above was subjected to a similarsolution treatment, cold rolled to a thickness reduction of 50 percent,aged at 500C for 1 hour and then cold rolled again to a thicknessreduction of 50 percent. The resulting alloy had a residual fluxdensity, Br, of 10,700 G and a coercive force, He, of 68 0e.

9. An alloy composed of 0.184 weight percent nitrogen, 10.30 weightpercent Mn, 9.23 weight percent Cr, 2.10 weight percent Mo, 10.65 weightpercent Co, and remainder iron was subjected to a solution treatment at1,050C, cold rolled to a thickness reduction of 83.5 percent, and agedat 550C for 1 hour. The resulting alloy had a residual flux density, Br,of 8,800 G and a coercive force, He, of X15 0e.

10. An alloy composed of 0. 1 89 weight percent nitrogen, 10.50 weightpercent Mn, 8.74 weight percent Cr, 1.86 weight percent Mo, 0.14 weightpercent C and re mainder iron was subjected to a solution treatment at1,050C, cold rolled to a thickness reduction of 65 percent, and aged at500C for 1 hour. The resulting alloy had a residual flux density, Br, of9,800 G and a coercive force, He, of 70 e.

1 1. An alloy composed ofO. l 68 weight percent nitrogen, 6.90 weightpercent Mn, 8.67 weight percent Cr l. A heat-treated permanent magneticalloy article consisting essentially of from about 02 to 0.4 weightpercent nitrogen, from about 9 to 12 weight percent manganese, fromabout 8 to 10 weight percent chroand remaindei; iron was sub ected to asolution treatmium, from about 1 to 3 weight percent molybdenum m at1050 C and Cold rond to a thlckness and the remainder iron, said weightsbased on the total of 9 Percent The resultmg alloy h resldHual weight ofthe article, said article produced by solution g g g of 6300 G and acoerclve orce treating the alloy at a temperature not lower than about 0I T l b 1 th h f 900C, cold rolling the treated alloy to a thickness rei is g i T i gzg gi gi fii g 10 duction from about 50 to 75 percent andthereafter t y g F C a ll aging the alloy at a temperature from about300 to 50- em W b r sys em a 0y W1 respec- O 0C, said alloy having aresidual flux density of at least What is claimed is:

"" 7 TABLE 1 Alloy Composition, treatment an Residual Coerciveprocessing flux density force Br Hc (gauss) (oersteds) This invention Mn10.12%, Cr 9.63%

Mo 2.10%, N 0.30l3%;

12300 59 cold rolled to a thickness reduction of 75%; aged at 500C.Cu-NiFe Fe Ni 20% Cu 60%; alloy rapidly cooled from 1000C. 2000 200 do.The alloy treated as above is 3200 400 aged at 650C.

do. The alloy having the above composition is cold rolled to a thicknessreduction of 95% and 5000 440 aged at 650C. Fe-Ni-Cr Ni 18%, 4%; alloycold rolled to a thickness 7000 reduction of 83%.

do, Ni 18%, Cr 8%; cold rolled to a thickness reduction of 93%. 800 178magnetic characteristics. It is clear from Table 1 that 9,000 gauss andexhibiting a coercive force less than the Fe-Mn-Cr system alloycontaining nitrogen accordb t 100 oersteads, ing to this invention hasexcellent characteristics. l l

